No one wants to have to give a dog back, of course, but you also need to know what your limitations are and what is practical for you depending on your personal situation. A lively puppy may not be a big deal if you live in a house, but it can be a nightmare in a small apartment. 

In your puppy search, steer clear of pet shops and puppy mills.  Unfortunately, pet shops are usually supplied by puppy mills.  These breeders do it purely for the money. 

They treat their dogs like livestock, keeping them in cages, breeding the females over and over again in order to produce more puppies.  

You might get  a good dog cheaply if it is a male, and many of the females end up in rescue when they are seven or eight and no longer able to produce large litters of pups. 

In some cases, they are ignorant of any knowledge about the dogs they breed, and give only a minimum amount of veterinary care.   

This could spell doom for your puppy if he is predisposed to any life-threatening diseases.  Veterinarians can perform preventive care on breeds that can suffer certain conditions.  You need to thoroughly research the breed of dog you are interested in, in order to become aware of any major cause of health concern before you get your puppy.